Instantaneous rate of change of a sphere

[ivysmerlin]

Homework Statement

Find the instantaneous rate of change of V with respect to r when r=5 micrometers

Homework Equations

V=4/3pi(r^3)

The Attempt at a Solution

would you just take the derivative? and if so, wouldn't it just be zero, because it comes out to be a real number, right? but that doesn't seem right...

 

[dlgoff]

What is the derivative of V=4/3pi(r^3)? Now what would the value be at r=5micrometers? Not zero.

 

[ivysmerlin]

ooh, I am an idiot, thanks